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Comments about microdata

From: Henri Sivonen <hsivonen@iki.fi>
Date: Wed, 13 May 2009 12:54:35 +0300
Message-Id: <F552DDAE-9634-43D9-AC05-0A2611867477@iki.fi>
To: "public-html@w3.org WG" <public-html@w3.org>
I like the new microdata draft. It addresses, or looks like it will  
address when there are vocabulary definitions, all the issues I've  
raised about microformats and RDFa over the years. Hopefully, it's not  
too late considering network effects.

- -

One of the most common points made in favor of RDFa in contrast to  
microformats is the ability to say things about external resources.  
Microdata in HTML5 has a predefined property called 'about'. However,  
it is rather awkward as a mechanism for saying things about external  
resources. I think it would be preferable to remove this predefined  
property and instead make an a, area, audio, embed, iframe, img, link,  
object, source, or video element imply its URI as the subject URI when  
the element is used as an item.

That is, this markup:
<img alt='Hedral the cat' src='http://www.example.com/hedral.jpg'  
id=hedral item> (Photo licensed under the <a href='http://creativecommons.org/licenses/by/3.0/' 
  itemprop='license' subject=hedral>Creative Commons Attribution 3.0  
Unported License</a>.
would generate the following triple:
<http://www.example.com/hedral.jpg> <http://www.w3.org/1999/xhtml/vocab#license 
 > <http://creativecommons.org/licenses/by/3.0/> .

In JSON, there could be a string entry with the key 'url' next to  
'type' and 'properties'.

- -

Considering the example above, it might be useful to consider an  
optimization allowing itemprops inside the legend of a figure to apply  
to the first embedded-content child of the same figure. (Yeah, this  
might be bad feature creep.)

- -

(Bikeshed alert.) itemprop and subject aren't in concordance. E.g.  
'prop' and 'subj' or 'p' and 's' would be.

- -

itemprop may take an 'absolute URL'. However, an 'absolute URL' is  
defined in terms of resolving onto itself and the algorithm for  
resolving URIfies URLs. Therefore, it seems that an absolute IRI  
cannot be an absolute URL. Since RDF seems to allow IRIs as properties  
and the current practice is to allow IRIs in various places, it seems  
to me that itemprop should take absolute IRIs instead of absolute URLs  
or the definition of absolute URL should be adjusted.

- -

Is there a reason why the value of various properties is taken to be  
the textContent as such without performing white space normalization  
(zapping leading and trailing white space and collapsing runs of white  
space into single U+0020)?

- -

Why doesn't the conversion to JSON expose top-level link relations,  
metadata items, cites and title? I think it should expose the same  
data as the RDF conversion (except perhaps lang, because annotating  
each value with lang in JSON would be cumbersome).

- -

When the <time> element is used to create a RDF literal, the literal  
should probably come with an appropriate datatype.

-- 
Henri Sivonen
hsivonen@iki.fi
http://hsivonen.iki.fi/
Received on Wednesday, 13 May 2009 09:55:19 UTC

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